The present disclosure relates to a propulsion unit for propulsion and maneuvering of a vessel, according to the preamble of claim 1. Especially, the invention relates to a propulsion unit provided with a nozzle exhibiting a curved following edge at the outlet of the nozzle.
There are known propulsion units including a propeller section which is fixed in a surrounding rotor part, in the periphery of which there are arranged permanent magnets or windings for providing magnetic field. The rotor part constitutes the rotor of an electrical motor and is positioned inside a surrounding stator part, which stator part is provided with magnetic devices or windings for generating magnetic field for causing rotation of the propeller section.
U.S. Pat. No. 5,220,231 discloses such a propulsion unit for a seagoing vessel. The propulsion unit has a centrally supported propeller section having propeller blades extending radially between a central part and a radially exterior positioned ring which rotates with a small radial distance from the stator part.
It is an increasing focus on reducing the power requirement for the use of all types of propulsion units for propulsion and maneuvering of a vessel. Higher demands regarding emission of environmentally unfriendly gases and fuel costs are increasing, something which have resulted in high focus on development of new solutions, among others, optimization of propeller blades and development of hybrid systems for propulsion of the vessels.
Another area where efforts have been made for improvement is on the nozzle of the propulsion unit.
GB1600994 discloses a fixed propeller nozzle having varying length extension of the nozzle through varying profile both on the inlet and outlet for the nozzle to exhibit reduced friction through improved hydrodynamic properties where the flow velocity is highest. Having a varying nozzle profile in front of the propeller, accordingly a curved inlet, will result in variations in the inflow to the propeller. Such a variation already exists from the hull and the solution in GB1600994 seeks to reduce this variation. Having such a varying nozzle inlet will require a lot of analyze work to adapt the nozzle inlet to a given hull. The same nozzle may on a different hull or application make bad matters worse. In other words, this solution is not adapted for mass production as it must be adapted to each vessel it is to be used on.
GB502564 describes a rotatable propeller nozzle which exhibits a varying length both in front and back of the nozzle, and exhibits a shape as an <<aircraft motor>> or ellipse-shaped to catch as much water as possible into the propeller.
It should be mentioned that it is most common to use a nozzle where a constant length is maintained around the entire nozzle, such as e.g. shown in U.S. Pat. No. 5,220,231. The main drawback with this is that the propulsion unit will require large space under the hull during rotation, and that it will result in a heavier propulsion unit.
It is therefore a need for providing a propulsion unit, preferably a rotatable propulsion unit, having lower weight compared to prior art, but which at the same time exhibits sufficient strength.
It is also a need for providing a propulsion unit exhibiting a larger inner space for supply of means for lubrication of bearing devices, something which the prior art does not solve.
It is further a need for providing a propulsion unit exhibiting improved properties for accommodating forces and vibrations than which is the case with prior art, which is especially present when the propulsion unit is pivoted out when the vessel is moving with high velocity.
It is common to use a permanent magnet motors in such propulsion units, something which results in that the nozzle in principle exhibit limited material thickness, which creates a need for a more solid nozzle to maintain an acceptable stress level in the material.